An electrical or hand-operated ratchet wrench has been heretofore used for positively and quickly tightening or removing bolts, nuts or the like. A conventional ratchet wrench is disclosed in U.S. Pat. No. 5,537,899 and the main structure thereof will be explained hereinafter with reference to FIGS. 12 to 19.
As shown in FIG. 12, a housing 10 is internally provided with a motor 12, a conventional motion conversion means 14 for changing rotational speed of the motor 12, and a crank shaft 16 which is mounted for rotational motion and reciprocating sliding motion by the motion conversion means 14.
As shown in FIG. 13, the crank shaft 16 is integrally formed at the extreme end thereof with a core 18 which is eccentric from the center of the shaft and parallel with the center of the shaft, and a bushing 22 having an insert hole 20 is slidably mounted on the core 18. As shown in FIGS. 12 and 14, the housing 10 is integrally formed at the extreme end thereof with a pair of annular holding portions 24, and an oscillating member 26 shown in FIG. 13 is provided between the pair of annular holding portions 24. The oscillating member 26 is formed in the center thereof with a hole 28, and the hole 28 is formed in the inner wall thereof with an internal gear 30. The oscillating member 26 has a pair of arms 32 at the extreme end thereof, and a space 34 is formed between the pair of arms 32. The bushing 22 is rotatably and undisengageably fitted into the space 34.
As shown in FIG. 15, a shank 36 for intermittently rotating bolts or the like comprises a columnar base portion 38 and a cubical engaging portion 40 formed integral with the base portion 38. The base portion 38 of the shank 36 is inserted into the hole 28 of the oscillating member 26. The oscillating member 26 with the shank 36 mounted therein is held between the pair of annular holding portions 24 of the housing 10 shown in FIGS. 12 and 14. As the crank shaft 16 rotates, the oscillating member 26 oscillates about the center axis of the hole 28.
In the shank 36, the columnar base portion 38 is internally provided with two wing members 44 which are oscillatable about a pin 42. Each wing member 44 is formed on both left and right ends thereof with a plurality of pawls 46. The columnar base portion 38 is formed with a central axial hole 48, and a columnar switching member 52 (FIG. 16) integrally formed with a switching knob 50 is fitted into the hole 48. The switching member 52 is mounted for rotation through a given angular range relative to the shank 36.
As shown in FIGS. 16 and 17, the switching member 52 is formed with two axially extending holes 54 with openings opposite each other by 180 degrees. Each hole 54 is internally provided with a tubular bushing pin 56 with one end closed, and one end open to receive a spring 58 internally to bias the bushing pin 56 outwardly from the switching member 52. As shown in FIG. 17, the closed end of the bushing pin 56 is biased by the spring 58 so as to project from the hole 54 into contact with the wing member 44, thereby pressing against the wing member 44.
The switching member 52 is normally and reversely rotated, for example, by approximately 90 degrees, when fitted into the hole 48 of the base portion 38 of the shank 36, by turning the switching knob 50 of the switching member 52, and the switching member 52 maintains one of the two stable positions shown in FIGS. 18 and 19. In FIGS. 18 and 19, each wing member 44 is pressed by the bushing pin 56 and the spring 58 so that the pawl 46 on one of left and right sides of each wing member 46 is engaged with the internal gear 30 of the oscillating member 26. In FIG. 18, the bushing pin 56 presses one side of the wing member 44 which oscillates about the pin 42. The part of the wing member 44 pressed by the bushing pin 56 is shifted from one side to the other of the wing member 44 by turning the switching knob 50 from the position shown in FIG. 18 to that of FIG. 19. By the switching with the switching knob 50, the pawl 46 of each wing member 44 meshed with the internal gear 30 of the oscillating member 26 is switched from one side to the other, thus switching between tightening rotation and loosening rotation.
When the oscillating member 26 is rotated in one direction with one pawl 46 of each wing member 44 engaged with the internal gear 30 of the oscillating member 26, wing members 44 move together with the oscillating member 26. On the other hand, when the oscillating member 26 is rotated in an opposite direction, the pawl 46 of each wing member 44 and the internal gear 30 of the oscillating member 26 come in contact but slip so that they are not engaged, and the wing members 44 will not move together with the oscillating member 26.
Thus, as shown in FIG. 18, when the oscillating member 26 is rotated in direction A, a tightening operation results, and when the oscillating member 26 is rotated in direction B slip occurs. In this manner, the tightening is carried out by repeating the tightening operation and the slip operation. Further, when switched from the FIG. 18 state to the FIG. 19 state, and when the oscillating member 26 is rotated in a direction C, the loosening operation results, and when the oscillating member 26 is rotated in a direction D, slip occurs.
As shown in FIGS. 12 and 14, the engaging portion 40 of the shank 36 is generally cubical in shape, and the engaging portion 40 projects, beyond one annular supporting portion 24 at the distal end of the housing 10, in a direction perpendicular to the length of the housing 14. A socket 60 for transmitting the intermittent rotational force of the ratchet wrench to the bolt or the like is detachably mounted on the engaging portion 40 of the shank 36. The socket 60 is cylindrical, and one end thereof is provided with a first hole 62 which is square in section for mating with the engaging portion 40 of the shank 36, and the other end thereof is provided with a second hole 64 which is hexagonal in section for fitting over a bolt (not shown). When the ratchet wrench is used, the socket 60 is mounted between the engaging portion 40 of the shank 36 and the bolt for tightening or loosening the bolt.
The operation of the ratchet wrench constructed as described above will be explained below.
First, when the motor 12 shown in FIG. 12 is driven, the crank shaft 16 is rotated through the known motion conversion means 14. When the crank shaft 16 is rotated, the core 18 of the crank shaft 16 causes the bushing 22 to rotate in a planetary orbit about the center axis the crank shaft 16. The planetary motion of the bushing 22 causes the oscillating member 26 to oscillate about the center axis of the columnar base portion 38 of the shank 36.
When the oscillating member 26 is oscillated in one direction, the pawl 46 on one side of the wing member 44 mounted on the shank 36 projects and is meshed with the internal gear 30 of the oscillating member 26 to rotate the shank 36 to tighten the bolt or the like (in direction A in FIG. 18). When the oscillating member 26 is oscillated in the opposite direction (B in FIG. 18), the projecting pawl 46 does not mesh with the internal gear 30 and the shank 36 is not rotated. Thereafter, when the oscillating member 26 is rotated in the one direction again, the bolt or the like is tightened. That is, in this ratchet wrench, only when the oscillating member 26 is rotated in one direction, is the shank 36 rotated, so that the bolt or the like is intermittently tightened.
In the ratchet wrench having two wing members 44, when the oscillation of the oscillating member 26 is slow, the pawl 46 of the wing member 44 moves along the internal gear 30 of the oscillating member 26 in a satisfactory manner, but when the oscillating member 26 is oscillated at high speed in order to enhance the working efficiency, a so-called resonant phenomenon caused by variation of oscillation speed occurs in the wing member 44, and "overshoot" occurs such that, as shown in FIG. 20, the pawl 46 of the wing member 44 being meshed with the internal gear 30 of the oscillating member 26 is temporarily moved away from the internal gear 30. When overshoot occurs, return of the wing member 44 into meshing engagement is delayed so that neither of the pawls 46 of the wing member 44 is meshed with the internal gear 30, resulting in a failure of the tightening operation.
When overshoot occurs, the pawl 46, on the side opposite the pawl 46 that should be meshed, sometimes becomes meshed with the internal gear 30 in a " " configuration commonly referred to as a "pigeon-toe" configuration, as shown in FIG. 21. In the state shown in FIG. 21, the shank 36 oscillates with the oscillating member 26, such that the tightening rotation is not produced at all.
In the case of operation at high speed, there is a point where the wing member 44 and the spring 58 begin to oscillate, and this oscillation is amplified (called a resonant point). This resonant point differs depending on the mass of the wing member 44 and the strength of the spring 58, but with high speed rotation there is always a resonant point. At the resonant point overshoot occurs, as described above and as shown in FIGS. 20 and 21, such that the tightening operation cannot be performed.
In the ratchet wrench, the switching member 52 is rotatably mounted on the shank 36, and the switching member 52 rotates along with the shank 36. When the shank 36 carries out the tightening rotation and stops suddenly upon completion of tightening, the switching member 52 incorporated into the shank 36 tends to further rotate due to inertia. At this time, in the case where reaction of the spring 58 is so small that the switching member 52 is not held by the spring 58, the switching member 52 will switch the wrench between the tightening operation and the loosening operation. To prevent such an unintended switching of the switching member 52, a strong spring 58 is employed.
For suppressing the overshoot phenomenon, in the conventional ratchet wrench, either a strong spring 58 is employed, or a stopper may be provided to limit motion of the wing member 44. Further, for preventing unintended switching, the spring 58 may be strengthened. However, in the case of the conventional small spring 58, its strength cannot be adequately increased. Further, while a stopper might be provided to prevent the wing member 44 from moving to an improper position, there is inadequate space for the stopper.
Accordingly an object of the present invention is to provide a ratchet wrench which is free of occurrence of overshoot and unintended switching.